Faculty: Genesis, bring in Butane.
Genesis: Ok, sir.
Faculty: If I have Butane, how would draw the new man projection for Butane. This is what will happen. Right? And now over here what type of Coformation do you have? Everything is completely eclipsing. The atoms which are present on the distill carbon, is that right? So, this is what called as eclipsed conformation of Butane. Because the CH3 on one carbon and the CH3 on the other carbon is exactly eclipsing. The H and H are completely eclipsing. So this is a complete or fully eclipsed conformation. And a fully eclipsed conformation for a butane is called as Syn. Yes, Syn.
Now, if I change the dihedral angle and rotate it by 60 degrees, you get something like this. Now what is the dihedral angle that I am talking about? Between CH3 and CH3, in the first Coformation, the angle was zero – was eclipsed. Now between CH3 of the first carbon and CH3 of the second carbon, the angle is 60 degrees. This is what is called your Gauche Conformation. Now if I further move it by 60 degrees, what would be the dihedral angle now? The dihedral angle will become 120 degrees. And at this point of time, what will it be called? It would be called as Eclipsed Coformation. But this Eclipsed is different from the Eclipsed or the SYN Coformation that we did. Because over here, CH3 is eclipsing a hydrogen and not CH3 and CH3. So this is also called as Eclipsed. Now if I move it by 60 degrees more, what is the dihedral angle now? The dihedral angle is 180 degrees. And this Coformation you get is called as the Staggered Coformation. And if you look carefully, that CH3 and CH3 are both exactly opposite to each other. So this is called as the Anti-Configuration. So Staggered – if it is fully staggered – it is called as Anti. Fully eclipsed is called as Syn. Now if I move it by 60 degrees more, what do you get? It’s again a Gauche Coformation. But if you look carefully, its exactly the opposite of the 2nd one. And then finally, you move it by 60 more degrees and this is the conformation that you would get. So these are the 5 different conformations that you get for Butane.
Can I get the 6th one? If I rotate it by 60 more degrees, what do you get? It comes back to the first one. So if the dihedral angle is zero degrees or 360 degrees, the conformations are same. So these are the 5 conformations of Butane.
Do you want to see how does it look like in the Saw-horse projection?
Students: Yes, Sir.
Faculty: Take a look. That is the Saw-horse projection for Butane. Now if I ask you out of all these conformations, which one is the most stable?
Faculty: Anti Conformation. Why exactly? Because the angle over there is 180 degree and CH3 is completely opposite to the other CH3.
So after Anti, you will get the Gauche Conformation. After Gauche, it would be the Eclipse conformation, which is not the fully eclipsed one. And finally the least stable would be the Syn Conformation. Now exactly similar to what we have done before.
Genesis, please plot the graph.
Genesis: Sure Sir.
Faculty: You get the graph. Now if you very carefully, this graph has 2 picks. Because we had 2 conformations which were similar. So it starts from the bottom, which is Anti, moves to the top, then comes to the bottom, then goes top and finally the bottom. This is how 5 confirmations are placed for the Butane. Now if you understand what Butane has for the conformations, drawing the conformations for any molecule would become very easy. All you have to do is, just focus on two carbons and everything else becomes a substitution. That’s it.